A morning stroll in Novato's 500-acre Rush Creek Open Space Preserve offers a medley of hiking pleasures - oak forest, wetland marshes, ridge views and bird-watching. Several trails lead to Cemetery Marsh, which, despite its gloomy name, is anything but somber. Bring water and a hat and start early to avoid the heat of the day. Bahia TrailGo through the gate and follow the wooden fence to the signed Bahia Trail. Little paths lead down to the water, where you may spot herons, egrets and possibly even a swan. Lichen hangs down over the trees, providing a slight air of mystery. From S.F. by car, take Highway 101 north and exit at Atherton Avenue/San Marin Drive, turning right onto Atherton Avenue. Gail Todd is the author of "Lunchtime Walks in Downtown San Francisco" and a tour leader for San Francisco City Guides.